Air and fuel staged burner

ABSTRACT

A burner ( 10 ) for reducing NO x  emissions where supply fuel ( 16 ) and supply air ( 20 ) are supplied to a combustion tunnel ( 52 ) at high and low velocities and secondary air ( 26 ) is supplied to a secondary combustion zone ( 60 ), wherein products of combustion ( 59 ) exiting into the secondary combustion zone ( 60 ) from the combustion tunnel ( 52 ) are drawn back into the combustion tunnel ( 52 ) and back into the secondary air conduit ( 54 ).

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of earlier filed UnitedStates Provisional Patent Application Ser. No. 60/171,073, filed Dec.16, 1999, entitled “Air and Fuel Staged Burner”.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to burners and, more particularly,to low NO_(x) emission burners having staged air and staged fuelcapabilities.

[0004] 2. Brief Description of the Prior Art

[0005] Low NO_(x) burners are known in the art. For example, U.S. Pat.Nos. 5,180,300 and 4,983,118 both disclose low NO_(x) regenerativeburners. Likewise, U.S. Pat. No. 4,732,093 to Hansen et al. discloses amethod and apparatus for burning fuel in an annular nozzle burner.However, there exists a need for a burner that further reduces NO_(x)generation.

SUMMARY OF THE INVENTION

[0006] The present invention provides an air and fuel staged burner thatreduces NO_(x) generation. One embodiment of a burner according thepresent invention generally includes a main burner body defining aninternal cavity, an air connection fluidly connected to the internalcavity, and a combustion tunnel. A distribution tee may be fluidlyconnected to the internal cavity defined by the main burner body and aburner nozzle may be positioned in the interior cavity of the mainburner body. The burner nozzle may define a primary air orifice, anannulus, and a fuel orifice. The air connection may be configured toreceive supply air and divide the supply air into primary air andsecondary air, where the ratio of primary air to secondary air isapproximately in the range of 40/60 to 70/30 respectively, with a 50/50ratio being preferred. The primary air preferably flows through theprimary air orifice at a rate of approximately 300-400 feet/second(91-122 meters/second).

[0007] The main burner body generally extends longitudinally about animaginary burner centerline, and the primary air orifice is preferablyoriented to form a convergent angle as measured from the imaginaryburner centerline, such as an angle of approximately 30-60° as measuredfrom the imaginary burner centerline. Alternatively, the primary airorifice may be oriented to produce a swirl pattern of primary air in thecombustion tunnel, where the swirl is approximately less than or equalto 0.7 times an internal diameter of the combustion tunnel.

[0008] The burner may also include a secondary air conduit fluidlyconnected to the distribution tee, the secondary air conduit having asecondary air jet fluidly connected to a secondary combustion zone. Themain burner body generally extends longitudinally about an imaginaryburner centerline and the secondary air jet is oriented substantiallyparallel to the imaginary burner centerline. Alternatively, the mainburner body may extend longitudinally about the imaginary burnercenterline with the secondary air jet oriented at an angle convergentwith the imaginary burner centerline. The secondary air exits thesecondary air jet at a velocity of approximately 150-400 feet/second(46-122 meters/second).

[0009] A fuel connector is configured to receive a supply fuel anddivide the supply fuel into a primary fuel and a secondary fuel. Thesplit ratio of primary fuel to secondary fuel split ratio isapproximately in the range of 20/80 to 40/60 respectively, with a splitratio of 22/78 being preferred. A primary fuel path and a secondary fuelpath may also be included, with the primary fuel path fluidly connectedto the annulus, the secondary fuel path fluidly connected to the fuelorifice, and the primary fuel path and the secondary fuel path fluidlyconnected to each other. The primary fuel may exit the annulus definedby the burner nozzle at a velocity approximately less than 100feet/second (30 meters/second). The secondary fuel may exit the fuelorifice defined by the burner nozzle at a velocity approximately greaterthan 350 feet/second. The fuel orifice and the fuel annulus may lie inthe same plane, substantially perpendicular to an imaginary burnercenterline and the distribution tee may be positioned adjacent to theinternal cavity of the main burner body and opposite the combustiontunnel (52).

[0010] One method of decreasing NO_(x) emissions in a burner having amain burner body defining a combustion tunnel may include the steps offlowing supply air into the main burner body, dividing the supply airinto primary air and secondary air, flowing the primary air into thecombustion tunnel at a given velocity, flowing primary fuel into thecombustion tunnel at a velocity lower than the velocity of the primaryair, flowing secondary fuel into the combustion tunnel at a velocityhigher than the velocity of the primary fuel, flowing secondary air intoa secondary combustion zone by a secondary air jet at a velocity higherthan the velocity of the primary fuel, and igniting the primary fuel,the secondary fuel, and primary air in the combustion tunnel to formproducts of combustion. Additional steps may include exhausting productsof combustion into the secondary combustion zone and drawing products ofcombustion into the combustion tunnel and into the secondary air jet.

[0011] The device and method according to the present invention helps toreduce burner NO_(x) emissions.

[0012] These and other features and advantages of the present inventionwill be clarified in the description of the preferred embodiment takentogether with the attached drawings in which like reference numeralsrepresent like elements throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a partial cross-sectional side view of one embodiment ofthe present invention;

[0014]FIG. 2 is a full cross-sectional side view of the embodiment shownin FIG. 1 excluding the secondary air jets for clarity and rotating thelocation of the primary air connection by 90 degrees; and

[0015]FIG. 3 is a front view of a burner nozzle shown in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016] The preferred embodiment of a burner 10 according to the presentinvention is shown in FIGS. 1-3. FIG. 2 shows the burner 10 having amain burner body 22 defining an air connection 12, an internal cavity13, and a combustion tunnel 52. A fuel connector 14 is provided throughwhich supply fuel 16 enters the burner 10, except in the event a gaspilot (not shown) is used through a port 18. An electrode (not shown) isused to ignite the burner 10; however, a gaseous pilot could be used.

[0017] As best shown in FIG. 2, supply air 20 enters the air connection12, passes into the internal cavity 13 defined by the main burner body22, and is divided into primary air 24 and secondary air 26. A secondaryair orifice 28 permits the secondary air 26 to enter a secondary airdistribution tee 30 while the primary air 24 passes through at least oneprimary air orifice 32 defined by a burner nozzle 46, with the number ofprimary air orifices 32 preferably in the range of four to eightorifices 32. The primary air 24 is accelerated through the primary airorifice or orifices 32 to a range of approximately 300 feet/second-400feet/second (91-122 meters/second), depending on the air preheatavailable, nominal burner 10 ratio, and rated input. The primary air 24is preferably directed in a convergent manner toward an imaginary burnercenterline C; however, the primary air orifice or orifices 32 may alsobe slightly offset to induce a swirl pattern on the primary air 24. Aconvergence angle a of the primary air orifice or orifices 32 can beapproximately 30°-60°, as measured from the imaginary burner centerlineC. The swirl or offset can be as much as 0.7 times the primary port, orcombustion tunnel, diameter D.

[0018] The supply fuel 16 entering fuel connector 14 passes into a fuelsparger 34 which divides the supply fuel 16 via holes 36 into primaryfuel 38 and secondary fuel 40. The primary fuel 38 travels along one ormore primary fuel paths 42, preferably parallel to the secondary fuel 40which travels through a secondary fuel path 44. The primary fuel path 42is preferably fluidly connected to an annulus 47 defined by the burnernozzle 46 positioned in the internal cavity 13 defined by the mainburner body 22. The secondary fuel path 44 is preferably fluidlyconnected to a fuel orifice 48, also defined by the burner nozzle 46.The primary fuel 38 exits the burner nozzle 46 through the annulus 47into the combustion tunnel 52 at a low velocity, ideally less then 100feet/second (30 meters/second), depending on rated input. The secondaryfuel 40 passes down the secondary fuel path 44 and exits into thecombustion tunnel 52 through fuel orifice 48, preferably accelerated toa velocity approximately greater than 350 feet/second (107meters/second), depending on rated input. As shown in FIG. 3, the fuelannulus 47 preferably has a first width W1 and the fuel orifice 48preferably has a second width W2, with the first width W1 of the fuelannulus 47 being less than the second width W2 of the fuel orifice 48.

[0019] Referring again to FIG. 2, the velocities of the primary and thesecondary fuels 38, 40 exiting the annulus 47 and the fuel orifice 48 ofthe burner nozzle 46 will depend on the velocity of the primary air 24exiting the primary air orifice or orifices 32. The primary fuel 38exiting the annulus 47 mixes in a highly turbulent region with theprimary air 24 exiting the primary air orifice or orifices 32, creatinga highly reducing combustion region within the combustion tunnel 52. Thesecondary fuel 40 exiting the fuel orifice 48 is accelerated to thepoint that there is only a partial mixing of the secondary fuel 40 withthe primary air 24 and products of combustion 59 in a primary combustionzone 50 of the combustion tunnel 52. Therefore, the profile ofcombustion exiting the combustion tunnel 52 is more oxidizing toward theperimeter of combustion tunnel 52 and more reducing along the imaginaryburner centerline C.

[0020] As best shown in FIG. 1, the secondary air 26 passes through thedistribution tee 30 and into a secondary air conduit 54. The secondaryair conduit 54 communicates the secondary air 26 to a secondary air jet56 spaced apart from a combustion tunnel exit 62 of the combustiontunnel 52 and in fluid communication with a secondary combustion zone60. Secondary air 26 exits the secondary air jet 56 at a velocity in therange of 150 feet/second to 400 feet/second (46-122 meters/second),depending on the air preheat, nominal design ratio of the burner 10, andrated input.

[0021] The burner 10 is capable of being operated with a singlesecondary air jet 56 or a plurality of secondary air jets 56. Thesecondary air jets 56 may be oriented parallel or convergent to theimaginary burner centerline C, shown as angle β in FIG. 1. The secondaryair 26 exits the secondary air jets 56 at a furnace wall 58 and createsa negative pressure region pulling the products of combustion 59 fromthe second combustion zone 60 back into the secondary air orifice 56,highly vitiating the secondary air 26 before the secondary air 26reaches the sub-stoichiometric ratio mixture exiting the combustiontunnel 52. The resultant combustion expansion in the primary combustionzone 50 of combustion tunnel 52 also creates a suction at the furnacewall 58 in the vicinity of the combustion tunnel exit 62 which alsoinduces the furnace products of combustion 59 back to the combustiontunnel exit 62.

[0022] The burner 10 configuration of the present invention providesvitiation in the primary and secondary combustion zones 50, 60 such thatthe stoichiometry to the burner 10 must be on the oxidizing side toinitiate stable combustion in the secondary combustion zone 60 whenbelow 1200° F. furnace temperature. At approximately 1200° F. (649° C.),the stoichiometry can be brought to approximately 10% excess air withthe resulting main flame stability and the secondary combustionreactions completing without the generation of free combustibles. Minortraces of CO will be apparent with furnace temperature between 1200° F.and 1400° F. (649° C.-760° C.). The primary fuel 38 to secondary fuel 40split ratio can be approximately 20/80 to 40/60, respectively, while theprimary air 24 to secondary air 26 split ratio can be 40/60 to 70/30,respectively. The optimum primary fuel 38 to secondary fuel 40 splitratio is approximately 22/78, respectively, and the optimum primary air24 to secondary air 26 split is approximately 50/50.

[0023] The air and fuel staged burner 10 according to this firstembodiment significantly improves NO_(x) emission capabilities, asillustrated in the following table: TABLE 1 COMPARISION OF PRESENTINVENTION WITH AN AIR STAGED BURNER AT AN AIR TEMPERATURE OF 750° F.(399° C.) AND A FURNACE TEMPERATURE OF 1600° F. (871° C.) AIR STAGEDFUEL & AIR STAGED NO_(x) PPM @ 3% 44 22

[0024] The invention has been described with reference to the preferredembodiment. Obvious modifications and alterations will occur to othersupon reading and understanding the preceding detailed description. It isintended that the invention be construed as including all suchmodifications and alterations.

We claim:
 1. A burner (10) for reducing NO_(x) emissions comprising: amain burner body (22) defining an internal cavity (13), an airconnection (12) fluidly connected to the internal cavity (13), and acombustion tunnel (52); a distribution tee (30) positioned adjacent tothe internal cavity (13) and spaced away from the combustion tunnel(52), the distribution tee (30) fluidly connected to the internal cavity(13); and a burner nozzle (46) positioned in the interior cavity (13) ofthe main burner body (22), the burner nozzle defining a primary airorifice (32), a fuel annulus (47) having a first width (W1), and a fuelorifice (48) having a second width (W2), wherein the first width (WI) ofthe fuel annulus (47) is less than the second width (W2) of the fuelorifice (48).
 2. The burner (10) as claimed in claim 1 , wherein themain burner body (22) extends longitudinally about an imaginary burnercenterline (C), and the primary air orifice (32) is oriented to form aconvergent angle (∝) as measured from the imaginary burner centerline(C).
 3. The burner (10) as claimed in claim 2 , wherein the convergentangle (∝) is approximately 30-60° as measured from the imaginary burnercenterline (C).
 4. The burner (10) as claimed in claim 1 , wherein themain burner body (22) extends longitudinally about an imaginary burnercenterline (C) and the primary air orifice (32) is oriented to produce aswirl pattern in the combustion tunnel (52).
 5. The burner (10) asclaimed in claim 4 , wherein the swirl is approximately less than orequal to 0.7 times an internal diameter (D) of the combustion tunnel(52).
 6. The burner (10) as claimed in claim 1 , further comprising asecondary air conduit (54) fluidly connected to the distribution tee(30), the secondary air conduit (54) having a secondary air jet (56)fluidly connected to a secondary combustion zone (60).
 7. The burner(10) as claimed in claim 6 , wherein the main burner body (22) extendslongitudinally about an imaginary burner centerline (C) and thesecondary air jet (56) is oriented substantially parallel to theimaginary burner centerline (C) of the main burner body (22).
 8. Theburner (10) as claimed in claim 6 , wherein the main burner body (22)extends longitudinally about an imaginary burner centerline (C) and thesecondary air jet (56) is oriented at an angle (β) convergent with theimaginary burner centerline (C) of the main burner body (22).
 9. Theburner (10) as claimed in claim 1 , further comprising a primary fuelpath (42) and a secondary fuel path (44), the primary fuel path (42)fluidly connected to the annulus (47), the secondary fuel path (44)fluidly connected to the fuel orifice (48), and the primary fuel path(42) and the secondary fuel path (44) are fluidly connected to eachother.
 10. A method of decreasing NO_(x) emissions in a burner (10)having a main burner body (22) defining a combustion tunnel (52) and asource of secondary air (26) comprising the steps of: a. exhaustingproducts of combustion (59) into a secondary combustion zone (60); andb. drawing products of combustion (59) from the secondary combustionzone (60) to an combustion tunnel exit (62) and to the source ofsecondary air (26).
 11. The method as claimed in claim 10 , furthercomprising the steps of: c. flowing supply air (20) into the main burnerbody (22); d. dividing the supply air (20) into primary air (24) andsecondary air (26); e. flowing the primary air (24) into the combustiontunnel (52) at a given velocity; f. flowing primary fuel (38) into thecombustion tunnel (52) at a velocity lower than the velocity of theprimary air (24); g. flowing secondary fuel (40) into the combustiontunnel (52) at a velocity higher than the velocity of the primary fuel(38); h. flowing the secondary air (26) into the secondary combustionzone (60) at a velocity higher than the velocity of the primary fuel(38); and i. igniting the primary fuel (38), the secondary fuel (40),and primary air (24) in the combustion tunnel (52) to form products ofcombustion (59).
 12. The method as claimed in claim 11 , wherein theratio of primary air (24) to secondary air (26) is approximately in therange of 40/60 to 70/30, respectively.
 13. The method as claimed inclaim 11 , wherein the primary air (24) flows into the combustion tunnel(52) at a rate of approximately 300-400 feet per second at rated input.14. The method as claimed in claim 11 , wherein the secondary air (26)flows in the secondary combustion zone (60) at a velocity ofapproximately 150-400 feet/second at rated input.
 15. The method asclaimed in claim 11 , wherein the primary fuel (38) to secondary fuel(40) split ratio is in the range of approximately 20/80 to 40/60,respectively.
 16. The method as claimed in claim 11 , wherein theprimary fuel (38) flows into the combustion tunnel (52) at a velocityless than approximately 100 feet/second at rated input.
 17. The methodas claimed in claim 11 , wherein the secondary fuel (40) flows into thecombustion tunnel (52) at a velocity approximately greater than 350feet/second at rated input.
 18. A burner (10) for reducing NO_(x)emissions comprising: a main burner body (22) defining an internalcavity (13), an air connection (12) fluidly connected to the internalcavity (13), and a combustion tunnel (52); a distribution tee (30)fluidly connected to the internal cavity (13); a burner nozzle (46)positioned in the interior cavity (13) of the main burner body (22), theburner nozzle defining a primary air orifice (32), a fuel annulus (47)having a first width (W1), and a fuel orifice (48) having a second width(W2), wherein the first width (W1) of the fuel annulus (47) is less thanthe second width (W2) of the fuel orifice (48); a fuel connector (14)defining a primary fuel path (42) and a secondary fuel path (44), theprimary fuel path (42) fluidly connected to the annulus (47), thesecondary fuel path (44) fluidly connected to the orifice (48), and theprimary fuel path (42) and the secondary fuel path (44) fluidlyconnected to each other; and a secondary air conduit (54) defining asecondary air jet (56), the secondary air conduit (54) fluidly connectedto the distribution tee (30) and the secondary air jet (56) spaced awayfrom the combustion tunnel (52).
 19. The burner (10) as claimed in claim18 , wherein the fuel orifice (48) and the fuel annulus (47) lie in thesame plane, substantially perpendicular to an imaginary burnercenterline (C).
 20. The burner (10) as claimed in claim 19 , wherein thedistribution tee (30) is positioned adjacent to the internal cavity (13)of the main burner body (22) and spaced opposite the combustion tunnel(52).